[Milsurplus] info on DA-515/U?

[eugene at hertzmail.com]

I picked up a DA-515/U Dummy Load at a hamfest. I understand it's rated
for 600W continuous, but does anyone know the specs for how long I can
run 1KW? I am looking for the duty cycle (you know, 2 minutes on, 10
minutes off, etc).

Is there a published rating curve for this? I believe it is equivalent
to the Bird 8400 series. I could not find the rating curve on bird's
website. I did find the manual, but it only mentions 600W continuous. I
tried to contact bird a month ago but no luck.

Anyone?
Thanks!
Eugene